# A multi-wavelength view of Active Galactic Nuclei with an emphasis on gamma-rays

## TL;DR

This paper reviews the diverse types of Active Galactic Nuclei across the electromagnetic spectrum, focusing on gamma-ray emissions, their underlying physics, selection biases, and future research directions with upcoming astronomical facilities.

## Contribution

It provides a comprehensive overview of AGN classes, emission processes, and the significance of gamma-ray observations, highlighting open issues and future prospects in AGN research.

## Key findings

- Different AGN types have distinct emission characteristics.
- Gamma-ray observations reveal unique insights into AGN physics.
- Upcoming facilities will enhance understanding of AGN phenomena.

## Abstract

Active Galactic Nuclei (AGN) are remarkable astronomical sources emitting over the whole electromagnetic spectrum, with different bands providing unique windows on distinct sub-structures and their related physics. AGN come in a large number of types only partially related to intrinsic differences. I highlight here the most important AGN classes, namely jetted and non-jetted, radiatively efficient and inefficient, and face-on and edge-on, the source types selected by different bands together with the most important selection effects and biases, and the underlying emission processes, emphasising the gamma-ray band. I then conclude with a look at some open issues in AGN research and at the main new astronomical facilities, which will provide us with new data to tackle them.